A huge storm just formed in the Atlantic, before hurricane season has even started

Hurricane season doesn’t start until June 1, but the National Hurricane Center announced Monday evening that Subtropical Storm Andrea had formed.

Called a subtropical storm because it has a blend of both tropical and nontropical characteristics, it is packing peak winds of 40 mph (64 kilometres per hour). The storm could strengthen slightly through Tuesday before weakening Wednesday and dissipating later this week.

It does not pose any threat to the United States.

It formed in an area of disturbed weather roughly halfway between the Bahamas and Bermuda. It has slowly become better organized over the past few days.

While it has been drifting west closer to the US East Coast in recent days, an approaching cold front is expected to nudge the weather patch north to northeast in the coming days – generally toward Bermuda.

The disturbance has a relatively short window to intensify into a named storm. By Wednesday, wind shear is forecast to become prohibitively strong for further development.

Track and intensity guidance from a series of simulations from the American global model. (weathernerds.org)

The subtropical storm makes 2019 the fifth consecutive year with a preseason named storm, following Ana in 2015, Bonnie in 2016, Arlene in 2017 and Alberto in 2018.

The trend over the past 50 years has been for the first named storm to form earlier and earlier, though there is a large spread.

(Brian McNoldy)

Above: Date of first named storm formation over the past 50 years. The official start of hurricane season is marked by the horizontal green line, and the median date of first formation is marked by the horizontal dashed black line.

The median date for the first named storm over that period (1969-2018) is June 23, but an objective measure of that spread called the “standard deviation” is a hefty 33 days.

Although the Atlantic hurricane season begins on June 1 and ends November 30, storms have historically formed in all months of the year.

The 2019 Atlantic hurricane season is predicted to feature near to slightly below normal activity overall.